A light emitting diode (LED) is a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, dopants in a doped region of the semiconductor can have predominantly electrons or holes, and is referred to either as an n-type or p-type semiconductor region, respectively. In LED applications, the semiconductor includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which cause the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light.
During operation, a forward voltage is applied across the p-n junction through a pair of electrodes. The electrodes are formed on the semiconductor material with a p-electrode formed on the p-type semiconductor region and an n-electrode formed on the n-type semiconductor region.
LED lighting typically uses phosphor materials to generate different color(s) from the LED and enhance color rendering index (CRI). An LED emits light with angle dependent intensity distribution. When a phosphor material is applied to an LED, it converts a portion of the light into a different color that is mixed with the unconverted portion. Depending on the angle, more or less light is converted, resulting in different colors after mixing. As perceived, the color, color temperature, and intensity of resulting light have an angle distribution. Additionally, due to multiple reflection at various interfaces, the light extraction efficiency is reduced.
Accordingly, what is needed is structure of an LED devices with phosphor coating and a method of making the same to address the above issues.